I think people are dubious about May-September relationships because the disparity in maturity makes it easy to manipulate and take advantage of the younger partner. THis is why companies and Universities have strong policies against such relationships. Some people believe that such relationships are, ipso facto, exploitative relationships, no matter what the people in them say.
In societies where plural marriage is allowed, these kind of relationships are more common. If you can afford to take care of them, every decade or so, you add a new wife. The same thing kind of happens in monogamous societies. The guy divorces his wife after she’s brought up the kids, and he marries someone new, and as young as his former wife was when they got married. Some men go through several generations of women this way.
Who knows what the truth is in any relationship? Maybe the older person is exploiting the younger for sex. We all want to be with someone who is beautiful and has a firm body. However, as we grow older, our bodies generally become more slack. If we’re mature, I think we learn to love each other through all the changes.
I suppose it’s possible to have an equal relationship with a high age disparity, but it is more difficult.